Can I Borrow That I'm Getting Married ?

Echoing everyone else, only if we were super close.

You don't wanna lend it to a so-so friend who will refuse to replace it if they lose/break it, and blame you for it b/c you should've made sure the clasp was tight or some bs like that.
 
My sister or my mother can borrow any of my jewelry, however, some have a lot of sentimental value and I would make sure to communicate that fact to them before lending it. As for a friend, I would have to know her and trust her like a sister. I've seen friends burned like tha too many times to not be careful about stuff like that.
 
If she was a true friend, not an acquaintance type friend, I totally would. Besides, aren't you supposed to borrow something to wear on your wedding day too? I think if it was a good friend, I would be honored that she would want to borrow something of mine. That's the sappy side of me though. :o)